1. Field of Invention
The invention relates to an optical disk drive and, in particular, to a servo control device for an optical disk drive and a servo control method thereof.
2. Related Art
With the advent of the information, video and audio age, the optical information storage technology has been widely used. When data is being accessed using this technology, a storage medium, such as an optical disk, and an optical disk drive for accessing the optical disk have to be utilized.
The optical disks that are often seen in the current market include a CD-ROM (Compact Disk Read Only Memory), a CD-R (Compact Disk Recordable), a CD-RW (Compact Disk Rewritable), a DVD-ROM (Digital Versatile Disk Read Only Memory), a DVD-RW/DVD+RW (Digital Versatile Disk Rewritable) and a DVD-RAM (Digital Versatile Disk Random Access Memory).
Among the conventional optical disks, the DVD-RAM is formed with a plurality of data tracks for recording data. FIG. 1 is a schematic illustration showing first to third data tracks 11 to 13 of a conventional DVD-RAM. Each data track includes several sectors to store the data, and a header Hd is disposed at a front end of each sector. The area formed by these headers Hd is referred to as an emboss area 20, which has a reflectivity higher than those of other areas of the optical disk.
Next, a TEZC (Tracking Error Zero Crossing) signal is usually utilized to perform a track seeking process in the conventional optical disk. In general, the TEZC signal has regular square waves, as shown in FIG. 2. The number of the square waves represents the number of data tracks of the optical disk crossed by the optical pickup head. For example, the TEZC signal from time t1 to t2 represents that the optical pickup head crosses two data tracks of the optical disk. The prior art utilizes the TEZC signal as the seeking signal, and the optical disk drive can obtain the number of data tracks of the optical disk crossed by the optical pickup head according to the seeking signal so as to control the moving speed of the optical pickup head.
However, when the optical pickup head moves to the emboss area 20 of the optical disk, a seeking error signal (TE signal) tends to have a glitch because the reflectivity of the emboss area 20 is much higher than the other areas of the optical disk. Thus, the corresponding TEZC signal in the emboss area 20 is affected by the TE signal and forms a plurality of square waves having a smaller frequency, as shown from time t3 to t4. In other words, the prior art utilizing the TEZC signal as the seeking signal tends to cause the seeking error, particularly in the emboss areas in DVD-RAM disk.
Therefore, it is important to provide a servo control device and a servo control method thereof for an optical disk drive capable of modifying the TEZC signal as a correct seeking signal.